Photo: NASA/JPL-Caltech
The Galaxy Evolution Explorer (GALEX), a space-based observatory surveying distant galaxies in ultraviolet light, has made an important discovery in our own Milky Way galaxy. Mira, a red giant star about 400 light years away from Earth in the constellation Cetus, has a tail of gas and dust that stretches 13 light years through space (this means that light emitted by Mira now won’t reach the other end of its tail until the year 2020). A tail like this has never been discovered around a star before.
Thousands of millions of years ago, Mira was a star like our own Sun, a main sequence star. When main sequence stars grow old, they expand to enormous size and cool. Mira has reached this stage, becoming a red giant which is gradually blowing its outer layers of gas away into space. Over time, it will become a planetary nebula and eventually die as a white dwarf – the hot, glowing remnant of a dead star’s core.
Mira is unusual, among stars in the Milky Way, in that it is moving very quickly with respect to the stars around it. It moves through space at 130 km/s, or 291,000 miles/hour. It is also a binary star – it has a white dwarf companion star (Mira B) and the pair of stars orbit slowly around each other as they move through space.
Mira’s tail is made of gas and dust which has been ejected by the star over the last 30,000 years, forming a wake behind it as it moves through the interstellar gas and dust of the Milky Way. Studies of the chemical composition of the tail, at different distances from the star, will offer a fascinating opportunity to learn about the processes of stellar evolution and mass-loss in red giant stars.
As a complete beginner, can you tell me where MIRA A is going to, if it is travelling at such a high speed and will it burn up before it hits something?
Comment by Victoria Kilkenny 22 August 2009 @ 10:25 pm
Hello Victoria,
Like our own Sun, Mira is in an orbit around the centre of our Milky Way galaxy. Stars like the Sun generally orbit the Milky Way within the disc of the galaxy but I believe Mira has a highly inclined orbit which carries it far above, and far below, the galactic plane. This might explain its unusually high speed relative to gas in the galactic disc.
The stars in the Milky Way are so widely spaced that they go through their entire lives, billions of years long, without ever running into each other. I imagine Mira will continue to orbit around the Milky Way, evolving as a red giant, steadily shedding gas from its outer atmosphere, until it dies as a white dwarf star.
You may find more information about high velocity stars, and Asymptotic Giant Branch giants like Mira, on the following wikipedia pages:
http://en.wikipedia.org/wiki/Stellar_kinematics
http://en.wikipedia.org/wiki/Asymptotic_Giant_Branch
http://en.wikipedia.org/wiki/White_dwarf
Comment by Jim O'Donnell 24 August 2009 @ 2:25 pm
Dear Jim, Thank you so much for your response to my question about MIRA A. It is quite humbling to know that we are just one small speck in such a vast space! My interest was prompted by the fact that MIRA A is a unique star in having a tail. There is a prophecy from San Damiano di Piacenza in Italy about just such a star. When the prophecy was given in the 1960s, people said it could not be true, because only comets had tails. Time has shown otherwise! I will e-mail the details, when I have looked up the actual wording and date.
Many thanks, Victoria
Comment by Victoria Kilkenny 30 August 2009 @ 10:31 pm
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Comment by Denny Paranada 25 January 2011 @ 4:15 am